Problem: Kevin is $3$ years older than Daniel. Two years ago, Kevin was $4$ times as old as Daniel. How old is Daniel now?
Explanation: We can use the given information to write down two equations that describe the ages of Kevin and Daniel. Let Kevin's current age be $k$ and Daniel's current age be $d$. The information in the first sentence can be expressed in the following equation: ${k = d + 3}$ Two years ago, Kevin was $k - 2$ years old, and Daniel was $d - 2$ years old. The information in the second sentence can be expressed in the following equation: ${k - 2 = 4(d - 2)}$ Now we have two independent equations, and we can solve for our two unknowns. Because we are looking for $d$, it might be easiest to use our first equation for $k$ and substitute it into our second equation. Our first equation is: ${k = d + 3}$. Substituting this into our second equation, we get the equation: $ {(d + 3)}{-2 = 4(d - 2)} $ which combines the information about $d$ from both of our original equations. Simplifying both sides of this equation, we get: $d + 1 = 4 d - 8$. Solving for $d$, we get: $3 d = 9$. $d = 3$.